Abstract. The heterogeneous processing of organic aerosols by trace oxidants has many
implications to atmospheric chemistry and climate regulation. This review
covers a model heterogeneous reaction system (HRS): the oleic acid-ozone
HRS and other reaction systems featuring fatty acids, and their derivatives.
The analysis of the commonly observed aldehyde and organic acid products of
ozonolysis (azelaic acid, nonanoic acid, 9-oxononanoic acid, nonanal) is
described. The relative product yields are noted and explained by the
observation of secondary chemical reactions. The secondary reaction products
arising from reactive Criegee intermediates are mainly peroxidic, notably
secondary ozonides and α-acyloxyalkyl hydroperoxide oligomers and
polymers, and their formation is in accord with solution and liquid-phase
ozonolysis. These highly oxygenated products are of low volatility and
hydrophilic which may enhance the ability of particles to act as cloud
condensation nuclei (CCN). The kinetic description of this HRS is critically
reviewed. Most kinetic studies suggest this oxidative processing is either a
near surface reaction that is limited by the diffusion of ozone or a surface
based reaction. Internally mixed particles and coatings represent the next
stage in the progression towards more realistic proxies of tropospheric
organic aerosols and a description of the products and the kinetics
resulting from the ozonolysis of these proxies, which are based on fatty
acids or their derivatives, is presented. Finally, the main atmospheric
implications of oxidative processing of particulate containing fatty acids
are presented. These implications include the extended lifetime of
unsaturated species in the troposphere facilitated by the presence of
solids, semi-solids or viscous phases, and an enhanced rate of ozone uptake
by particulate unsaturates compared to corresponding gas-phase organics.
Ozonolysis of oleic acid enhances its CCN activity, which implies that
oxidatively processed particulate may contribute to indirect forcing of
radiation.